We had one of our Exchange mailbox databases become corrupt and it was in a "dirty shutdown" state. We worked with Microsoft however it ended up that we had to restore the mailboxes on that database from backup from the night before.
After the restoration of the mailbox database, whenever users on this database try to send and update to a calendar invite they are receiving an error message that states "You do not have permission to send the message on behalf of specified user".
I have tried setting the "NT AUTHORITY\USER" permission for Full Access and Send As permissions to ensure that the user has full access on their mailbox and items.
Thanks for your assistance!